An experimental and analytical study on intermittent slot die coating of viscoelastic battery slurries

Large-scale secondary lithium-ion batteries could be a key technology to compensate for the inconsistent energy supply of renewable sources. However, their manufacture is still very costly. In particular, the intermittent slot die coating of the battery electrodes is the speed-limiting and thus cost-driving process. In this field, various patents have been granted, and most in-house coating equipment was developed in industry. These technologies are often optimized empirically, since intermittent slot die coating is not mentioned in the scientific literature. In this work, we investigate the dominating and limiting mechanisms for intermittent slot die coating of non-Newtonian battery slurries. To characterize the process, we measured the system and die pressure and the associated wet film thickness. To build a common basis for all established technologies, we reduced the coating system to a syringe pump, a bypass valve, and a slot die. Our results show the direct link between casted film and pressure distribution within the coating. To reduce leveling times between the coating and interruption phases of an intermittent coating, a model was developed to predict the optimum pressure levels. It was found that different pressure levels during the coating and interruption phases lead to film break-ups or downstream die swelling, and thus limit the whole process.